The present invention relates to a process for removing ink from wastepaper in order to provide paper pulp that may be reused to manufacture new paper-based products. In particular, the invention is directed to a process for removing both water-based and oil-based inks from wastepaper by means of a novel group of deinking agents. 2. Description of the Prior Art
Recycled wastepaper has traditionally been a source of raw fiber materials needed in the papermaking industry. In the past, fiber from wastepaper was only employed in the production of low grade paper and paperboard products. Today, however, reclaimed fiber comprises about 25 percent of the total fiber used to manufacture paper, thereby providing an incentive for improving the utility of reclaimed paper pulp materials. In particular, recent efforts have attempted to develop techniques for effectively removing ink from waste fibers, in order to permit their use in the manufacture of high quality paper.
In conventional paper reclamation processes, deinking is carried out by converting the wastepaper to a pulp and contacting the pulp with an alkaline aqueous deinking medium containing a chemical deinking agent, in order to remove ink and other impurities from the pulp fiber and produce a suspension or dispersion of the ink and other particles in the aqueous medium. The resulting mixture is subsequently treated to separate the suspended ink and other particles from the pulp, for example, by air sparging and floatation of the ink/deinking agent complex, followed by skimming to remove the ink and other particles from the treatment bath, or by filtration and subsequent water washing of the fiber mat to remove dispersed ink particles.
There have been numerous attempts in the prior art to improve the efficacy of conventional deinking processes. For example, U.S. Pat. No. 4,618,400 discloses a method for deinking wastepaper which involves converting the wastepaper to a pulp; contacting the pulp with an aqueous medium of alkaline pH containing about 0.2 to 2% by weight of a deinking agent which is one or a mixture of certain thiol ethoxylate compounds; and removing suspended or dispersed ink from the pulp-containing medium.
U.S. Pat. No. 4,666,558 illustrates a deinking process for waste newsprint, which involves contacting and agitating a pulped newsprint in an aqueous medium containing a deinking agent comprising a particular mixture of a water-soluble C.sub.9 to C.sub.16 alkanol ethoxylate component and an oil-soluble C.sub.9 to C16 alkanol ethoxylate component, and recovering deinked pulp from the aqueous medium.
U.S. Pat. No. 3,932,206 describes deinking agents which are said to be non-toxic to aquatic life; the disclosed compounds consist of ethoxylated aliphatic mono-or diols.
Japanese Patent Publication 59-150191 discloses a process for deinking wastepaper by macerating the paper in the presence of a fatty acid salt, and then subjecting the paper to a quaternary ammonium surfactant.
Soviet Union Patent 926129 provides a composition for removing printing ink from wastepapers, which contains quaternary ammonium and phosphonium surfactants, isoamyl alcohol, phosphine oxide, butyl xanthogenate, and solvent.
U.S. Pat. No. 4,867,844 discloses a method of treating fibrous materials, by applying an organophilic complex formed from a clay (preferably bentonite) and an organic radical derived from an onium compound (preferably quaternary ammonium compound).
Japanese Patent Publication JP3119189 discloses a method of removing fibrous contaminates from the white water resulting from paper making by separately adding clay and a cation-surface-active bonding agent. The bonding agent disclosed is stearyl-trimethyl ammonium chloride.
Despite the foregoing efforts, it is generally agreed that no completely acceptable process for deinking wastepaper presently exists. One shortcoming of many of the prior art deinking techniques is the inability of these processes to simultaneously remove both water-based and oil-based inks from the wastepaper. The removal of water-based (flexographic) inks from wastepaper has proved to be a particularly troublesome problem associated with known flotation deinking processes. For example, standard fatty acid soap chemistry cannot collect the highly dispersed water-based ink waste. The removal of water-based inks from wastepaper using washing deinking processes also presents problems because of the use of large volumes of water and the need to treat the water so that the water can be recycled. In this regard, substantial costs are associated with processing wastepaper materials to separate water-based ink containing materials from those which contain oil-based inks.
Moreover, deinking agents utilized to date have been ineffective in removing tacky contaminants from wastepaper. These tacky contaminants (from pressure sensitive labels, binding materials and glues) are frequently encountered in wastepaper deinking processes, and tend to limit the quality of the final recycled product.
It would therefore be highly desirable to provide a process for deinking various types of wastepaper which contain water-based and/or oil-based inks. In addition, it would be advantageous if such a deinking process could also remove tacky contaminants from the treated wastepaper, in order to enhance the quality of deinked paper pulp yielded by the process.